Statement of Changes in Stockholders' / Members' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock Class A common stock	Common Stock Class B common stock	Treasury Stock Class A common stock	Members' Equity	Additional Paid-in-Capital	Retained (Deficit) Earnings	Non-controlling Interest	Total
Balance at Dec. 31, 2012				$ 428,400				$ 428,400
Increase (Decrease) Stockholders' Equity
Sale of common stock	$ 13	$ 37			$ 172,431			172,481
Sale of common stock (in shares)	12,500	36,836
Reclassification of members' contributions				(464,037)			$ 464,037
Stock-compensation expense				10,100	738			10,838
Distribution to members				(10,000)				(10,000)
Net income (loss)				$ 35,537		$ (2,186)	(10,946)	22,405
Balance at Dec. 31, 2013	$ 13	$ 37			173,169	(2,186)	453,091	624,124
Balance (in shares) at Dec. 31, 2013	12,500	36,836
Increase (Decrease) Stockholders' Equity
Treasury Stock			$ (358)					(358)
Treasury Stock (in shares)	(23)		23
Exchange of Class B Shares for Class A Shares					1,554		(1,630)	(76)
Exchange of Class B shares for Class A shares (in shares)	117	(117)
Stock-compensation expense					4,040			4,040
Vested restricted shares (in shares)	28
Net income (loss)						41,136	184,484	225,620
Balance at Dec. 31, 2014	$ 13	$ 37	$ (358)		178,763	38,950	635,945	853,350
Balance (in shares) at Dec. 31, 2014	12,622	36,719	23
Increase (Decrease) Stockholders' Equity
Sale of common stock	$ 12				123,189			123,201
Sale of common stock (in shares)	12,263
Exchange of Class B Shares for Class A Shares	$ 6	$ (6)			54,209		(92,393)	(38,184)
Exchange of Class B shares for Class A shares (in shares)	5,446	(5,446)
Stock-compensation expense					7,562			7,562
Stock-compensation expense (in shares)	67
Vested restricted shares (in shares)	153
Net income (loss)						(2,381)	(6,696)	(9,077)
Balance at Dec. 31, 2015	$ 31	$ 31	$ (358)		$ 363,723	$ 36,569	$ 536,856	$ 936,852
Balance (in shares) at Dec. 31, 2015	30,551	31,273	23